The proposed studies are intended to provide data showing the feasibility of developing a bacteria-laser system for detecting and measuring the toxic response from chemical exposure at levels failing to produce acute symptoms, but possibly causing detectable damage years later. A battery of isogenic Bacillus subtilis strains with mutations in various DNA or chromosomal repair steps, and capable of identifying specifial chemical classes, will be used to screen high priority pollutant chemicals for their cytotoxicity and DNA-damaging effects. From the battery of more than 20 mutants, a smaller set consisting of strains shown to detect the greatest number of substances and to respond with the highest level of specificity, will be selected for use in a differential light scattering (DLS) assay. The B subtilis repair battery, has been applied to a wide variety of chemical substances alleged to cause adverse health effects and for which a mode of action is known. The system will use a monochromatic laser source to illuminate the B. subtilis (bacterial) cell suspensions in a clear curvette. An array of detector elements arranged so that they will receive the scattered light at a series fo discrete angles will measure DLS intensity. Since each element will measure the scattered light intensity at a different angle relative to the incident beam, a unique DLS pattern will be generated, based on the size and shape characteristics of cells in the suspension. A computer programmed plot of the log relative intensity versus the scattering angle will record the pattern of unexposed cell suspensions and cell suspensions exposed to the test material at various concentrations. Since changes such as cell shrinkage, enlargement, division or lysis will generate unique DLS pattern deviations, a toxicity response will be detected within the span of a single generation (approximately 60 min). For each sample analyzed by this procedure, compound-specific dose responses will be validated by bacterial liquid and plate DNA-damaging/cytotoxicity assays and by conventional procedures of analytical chemistry. Phase I R&D is expected to lead to development of a portable instrument for rapidly assaying and tentatively identifying a wide range of toxic agents in the environment; useful in monitoring water supplies, workers exposed to potentially hazadous chemicals, air particulates or leachates from toxic waste sites and the toxicity of chemicals from many environmental sources.